An active noise control apparatus (referred to as an “ANC apparatus” hereinafter) is known as an apparatus for controlling sound related to vibration noise in a vehicle interior. The ANC apparatus outputs a canceling sound of a phase opposite to that of the vibration noise from a speaker inside a vehicle interior to reduce the vibration noise. An error between the vibration noise and the canceling sound is detected as a residual noise by a microphone disposed near an ear of a vehicle occupant and is used for determining the canceling sound at a later stage. The ANC apparatus reduces the vibration noise (muffled engine sound) generated in the vehicle interior in accordance with an operation (vibration) or the like of an engine installed in a vehicle, or reduces the vibration noise (road noise) generated in the vehicle interior in accordance with a contact between wheels and a road surface while the vehicle is running. Generating mechanism of the road noise is very complicated, however, a path for the road noise to reach to an ear of a vehicle occupant can be exemplarily illustrated as in FIG. 6.
In order to calculate the canceling sound for the road noise, some of the ANC apparatus that attenuate the road noise employ one or more acceleration sensors provided on a suspension for detecting the vibration of the wheel (Japanese Laid-Open Patent Publication No. 05-265471, Japanese Laid-Open Patent Publication No. 06-059688, Japanese Laid-Open Patent Publication No. 06-250672 and Japanese Laid-Open Patent Publication No. 07-028474). Such ANC apparatus apply adaptive control processing to a base signal based on detected values of the acceleration sensors and outputs the canceling sound in accordance with a control signal generated by the adaptive control processing. In the adaptive control processing, the amplitude of the base signal is adjusted so that an error between the vibration noise and the canceling sound is minimized.